Hawaiʻi’s Anchialine Pools

Anchialine pools are relatively rare worldwide but common on Hawaiʻi Island (and also occasionally on Maui and Oʻahu). The term “anchialine” comes from a Greek word meaning “near the ocean,” and in Hawaiʻi they are considered wetlands that are “landlocked” and only connected to the sea through underground lava tubes, tunnels, cracks and karst (porous limestone) barriers.  These pools are sometimes referred to as “loko waikai” in Hawaiʻi because they are brackish – have inputs of fresh groundwater (wai) and saltwater (kai) – or are also known as “loko wai ʻōpae” for the famous anchialine pool shrimp that dwell in many of these ecosystems.

Anchialine pools are unique, fragile habitats that are home to numerous native wildlife species, including ʻōpae ʻula (Halocaridina rubra or “red shrimp”), that as of May 2025 was officially designated the state shrimp of Hawaiʻi. These ecosystems also support seven other anchialine shrimp species (half of which are endemic to Hawaiʻi and two that are endangered), plus an endangered crab (Pele ramseyi) and a rare endangered eel (Xenoconger fryeri). Plus, anchialine pools are an important source of drinking water and invertebrate food resources for our resident waterbirds, visiting migratory shorebirds, the ʻōpeʻapeʻa (endangered Hawaiian hoary bat), and pinao (damselflies and dragonflies, including some protected species). Anchialine pools also provide habitat for rare flora like mauʻu ʻōpae (Ruppia maritima, widgeongrass) and a diverse community of cyanobacteria (blue-green algae) mats. The shrimp have a symbiotic relationship with the cyanobacteria, and the species present are often distinct between certain pool systems.

How Hawaiʻi Wildlife Fund Works to Help Anchialine Pools

HWF has been working to protect Hawaiian anchialine pools since the mid 2000s. For over a decade, we have been actively working to restore anchialine habitats in Kaʻū, Kona, and Kohala (on Hawaiʻi Island).  Plus, we have participated in multiple island-wide gatherings, statewide workshops, and international conferences focusing on anchialine ecosystems since that time. Learn more about our contributions during International Symposia on Anchialine Ecosystems (ISAE) in the resources section below, including co-hosting the 5th International event in Kona in November 2022.

Anchialine pools and fauna in Hawaiʻi are faced with many threats from coastal development, sea-level rise and the introduction of invasive species. They are also resilient and can recover and thrive when habitat modifying invasive species and other critical threats are removed. Development can directly damage habitats by filling them in or impacting water quality and freshwater quantity. Sea-level rise and increased flood activity caused by climate change can transition anchialine pools into tidepools (devastating habitat) and push pool systems up mauka (upland) to less optimal habitat. Invasive plant species like pickleweed (Batis maritima) and seashore paspalum (Paspalum vaginatum a.k.a. golf-course grass) can overgrow ecosystems and add leaf litter. Some invasive fish species including guppies and tilapia directly predate on native species like the ʻōpae ʻula, and can severely limit their population in affected pools. Learn more about the impacts of invasive species on brackish ecosystems in Hawaiʻi in this YouTube video. Plus, both invasive plants and animals can contribute excess sediments to pool habitats that can lead to ecosystem senescence (loss by aging).

Our own journey into anchialine restoration activities began in Waiʻōhinu in 2009 within the Kaʻū Forest Reserve. The restoration team started with invasive vegetation removal and followed up with sediment removal from the Hoʻonoua anchialine complex. Since then, HWF has been working with state, federal, business and nonprofit partners to secure permits needed to finalize fish (invasive tilapia) removal from these pools – which are devastating the ʻōpae ʻula population where they exist.

Plus, our dedicated HWF mentors love to teach about anchialine fauna! In fact, anchialine pools are one of the focus habitats of our Hawaiian Coastal Ecosystems unit (geared towards grades 6-8) that we provide in classrooms across Hawaiʻi Island and remotely. Learn more on our Youth Education page and please contact us to schedule a visit to your school!

Partnering to Protect Anchialine Pools

HWF is working with state and nonprofit partners to reduce and remove threats to anchialine habitats, and to bring greater awareness to this critical coastal ecosystem. In 2019, working with fellow members of the Hui Loko: Hawaiʻi Island Fishpond & Anchialine Pool Caretaker Network (coordinated by The Nature Conservancy of Hawaiʻi), we helped to introduce legislation to nominate the ʻōpae ʻula as the State Shrimp of Hawaiʻi.  Introduced by Representative Nicole Lowen and 19 other state legislators, the bill sat idle and was never scheduled for a hearing.

In 2025, the bill was re-introduced by Rep. Lowen and colleagues with additional support and advocacy from our partner, Kuaʻāina Ulu Auamo (KUA), and was passed through the House and Senate with unanimous supportive testimony. The bill passed into law on May 19, 2025 with Governor Green’s signature (Act 71) and the ʻōpae ʻula is now officially our state shrimp! We are looking forward to increased conservation efforts and educational opportunities centered around this important species and its anchialine habitat.

Furthermore, it is important to remember that these pools and inhabitants were (and remain) of utmost importance to the people of Hawaiʻi. As we work to restore (and protect) these ecosystems we are also reconnecting community members with these wahi pana and building new connections and stewardship opportunities into the future. As was shared with us by one of the co-founders of the Hui Loko network:

“Native Hawaiians cultivated a deep kinship connection with these precious pools and cared for them in a number of ways including keeping their perimeter free of encroaching vegetation, building walls, steps, and natural structures to facilitate healthy habitat, and regulating harvest through sound kapu and kanawai. The fauna of anchialine pools supported a thriving sustainable fishery for ʻōpelu which were fed, trained, and harvested seasonally in ocean waters. The fishing practice of north Kona involved making palu, or bait from ʻōpae ʻula and mud or cinder to attract ʻōpelu in specific areas of convergence in the ocean called koʻa. Skilled fishers spent significant time feeding ʻōpelu until they learned to aggregate in these areas. When they reached sufficient size and abundance, they were harvested to feed an entire community and some were released to train next year’s fish. This practice was sustained for hundreds of years, feeding thousands of people, while ensuring abundance.” – Chad Wiggins / Hui Aloha Kīholo